Note: For CONA, built works include structures or parts of structures that are the result of conscious construction, are of practical use, are relatively stable and permanent, and are of a size and scale appropriate for, but not limited to, habitable buildings. Models and miniature buildings are not built works (they are movable works). Most built works in CONA are manifestations of the built environment that are typically classified as fine art, meaning it is generally considered to have esthetic value, was designed by an architect (whether or not his or her name is known), and constructed with skilled labor. However, other structures that do not fall under this definition may also be included. Historical works, or works that were planned but never executed, are placed in the Movable Works or here in Built Works hierarchies, because they were, or were intended to be, physical entities, not merely conceptual in nature; for multiples, place them under Conceptual Works.